Among image processing technologies, a technology for reducing a random noise contained in an image is indispensable to reproduce a captured image more clearly. The technologies for reducing a random noise include one disclosed in PTL 1, for example.
The technology described in PTL 1 is comprised of, for an arbitrary pixel of interest ‘i’ in a color digital signal in a primary scan direction output from an input image processing circuit, a plurality of calculation circuits for calculating a number of moving average pixels ‘n’ based on a predetermined equation; a plurality of bit selection circuits for selectively outputting the pixel of interest ‘i’ and ‘n’ reference pixels ‘j’ preceding and following the pixel of interest ‘i’; a plurality of differentiation circuits for calculating an absolute value of a difference between an output level of the pixel of interest ‘i’ and an output level of each reference pixel ‘j’; a plurality of decision circuits for outputting the pixel of interest ‘i’, comparing a value output from the plurality of differentiation circuits with a predetermined threshold in a threshold storage memory, and outputting the reference pixel ‘j’ based on a result of said comparison; and a plurality of calculation circuits for performing moving average processing on output signals from the plurality of decision circuits.
In other words, since it is configured to add a reference pixel ‘j’ to moving average processing only when the absolute value of the difference between the output level of the pixel of interest ‘i’ and the output level of the reference pixel ‘j’ is equal to or smaller than a threshold, a portion in which the absolute value of the difference changes sharply beyond the threshold is excluded from the moving average processing, and noise components can be thereby effectively removed.